Air cushion, hovering-type lawnmowers have long been known, for example U.S. Pat. Nos. 3,110,996, 3,756,336, 3,452,523. In these constructions the cutting blade rotates with a high, constant rate of revolution in order to seize the grass and then to cut or chop it up. Furthermore, the grass is repeatedly drawn into the cutting zone by the air back pressure of the mower air cushion, and cut up repeatedly until finally only a mulch of finely chopped up grass remains on the ground.
In connection with the above procedure, it is recommended that the lawn be mowed twice weekly, that is about every three days. If, in fact, this three day interval is exceeded, serious difficulties arise with the mowing procedure because the grass becomes too long and can no longer be completely chopped up, so that it becomes necessary to recut the grass. This after treatment is carried out by mowing the whole lawn surface once again with the air cushion lawnmower, or a conventional rotary mower, in order to further chop up the only partially cut grass. After that, the grass cuttings have to be raked away with a special sweeping machine or with a rake.
It can, thus, be seen that the use of the known air cushion lawnmower, because of the frequent mowing and/or because of the necessity to clear away the mown grass, is very time consuming.
It is well known that some wheeled lawnmowers are provided with a grass catching device, such as a grass receiving sack, so that in itself the mowing intervals could be lengthened but no basic improvement is achieved with this arrangement. This is because the mowing operation must be frequently interrupted in order to empty the grass receiving device. In addition, the connecting channel between the lawnmower and the grass receiving device easily blocks up, especially with damp grass. Moreover, the handling of such wheeled lawnmowers equipped with grass receiving devices is unwieldy and laborious.
Furthermore, in the use of the known air cushion lawnmowers there are additional difficulties in that the blunt striking or chopping blade is sharpened for only about 4 cm at the ends thereof and the constant rate of revolution of the blade does not allow a perfect mowing for all kinds of lawns and for all types of lawn conditions, such as, hard, soft, thin, thick, long or short grass, nor for all types of weather conditions, such as, damp or wet grass. The individual problems herein set forth for air cushion lawnmowers also occur basically with respect to wheeled lawnmowers.
It is an object of the invention, in view of the above mentioned problems, to provide a rotary lawnmower, the use of which avoids a time consuming after treatment of the mown lawn surface, even in the case of a lawn which is in itself difficult to mow, in particular, a lawn which has not been mown for a long time. The end result is a more effective mowing of the lawn.
Another object of the present invention is to provide at least one grass clearing plate on the lawnmower housing. In a particularly advantageous embodiment, the grass clearing plate protrudes at a distance from the forward frontal side of the mower housing, in the direction of the working movement of the mower, such that the housing surface between the edge of the housing and the grass clearing plate forms a loading surface for the cut grass.
The substantial advance achieved by the present invention is that the mowing and grass clearing occur at the same time so that a separate after treatment of the cut lawn, especially by raking up or use of a sweeping machine, is unnecessary.
The basic construction of the invention envisions a single grass clearing plate that is detachably mounted, as required, on the front side or rear side of the lawnmower. The direction of movement chosen for the air cushion lawnmower depends on the grass itself and the weather conditions. However, with very wet grass, thin and fine grass, or in dry weather conditions, the lawnmower is moved backwards, or in the pulling direction, whereas with thick and high grass, it is moved forwards or in the pushing direction. In the case of an air cushion lawnmower, a single grass clearing plate is sufficient for all types of lawn and weather conditions, without it having to be transferred between the front and rear side of the lawnmower housing. Moreover, it is preferable to provide means for mounting the pushing handle on both sides of the lawnmower housing to thereby adjustably fasten the pushing handle in the length direction of the lawnmower.
In the case of mowing wet, thin and light types of grass, the pushing handle is mounted on the front half of the lawnmower housing, so that the hovering air cushion lawnmower is automatically lightly pressed forwards and can better take up the grass swaths lying lower on the ground, whereas for dry and very long grass, the pushing handle is secured on the rear half of the housing.
Mowing and grass clearing can thus, with this embodiment of the invention, be achieved under all conditions, in a single direction, if merely the fastening of the pushing handle is varied in the length direction of the housing.
Pursuant to the teachings of the present invention, it is now possible to mow the lawn, at much longer time intervals, for example of nine days, indeed even about three weeks, without a time consuming after treatment of the lawn being necessary.
With the grass clearing plate provided according to the present invention, it is appropriate, when mowing a given lawn surface in a path of concentric rectangles from the outside towards the inside, and during mowing on any particular turn of any rectangle at the same time to clear or push the grass swaths lying on the immediately adjacent outer rectangle automatically to at least one of the diagonals of the lawn surface. Thus, on completion of mowing, one or two crossing diagonals of grass swaths remain, which are then pushed together by the lawnmower with its grass clearing plate to provide a single pile of grass clippings which can be transported away in the conventional manner. It will be evident that an appreciable time saving can be achieved by the present construction so that now only about a third of the time previously needed to mow a lawn is required.
Surprisingly, it has been found that the clearing away of the mown grass is further facilitated if the grass pile formed by the pushing and clearing up process with the grass clearing plate according to the invention cling together rather firmly, which can be attributed to the unordered, random tangle or felting of the cut grass clippings in the individual piles.
It is preferred to construct the grass clearing plate integrally with the lawnmower housing, for example, of plastic. The grass clearing plate can, however, also be detachably fastened to the lawnmower housing, in particular for subsequent mounting on conventional lawnmowers; but also on lawnmowers to be newly manufactured. Furthermore, the grass clearing plate is adapted, in a simple manner, to be adjustable by means of an adjustable detachable fastening on the lawnmower housing according to the type and condition of the lawn, and also according to weather conditions.
The collection of the cut grass is facilitated if the lawnmower housing adjacent to the grass clearing plate has a flattened, smooth edge, bent slightly downwards, which extends over at least a part of the width of the housing. In order to accomplish this, it is appropriate that the flattened, smooth edge on the front or pushing direction side of the lawnmower extends over only about one third of the width of the housing to the grass ejection side.
In the above manner, as has been shown in practical use, reliable mowing can also be achieved with differing types of lawn and ground formations, as well as wet or dry, thin or hard grass. Moreover, by flattening of the edge over only about one-third of the width of the housing, seizing up of the lawnmower in dry weather, as well as with hard and thick grass, is almost completely eliminated.
It is preferable that the length of the smooth edge, flattened over the full width of the housing, on the rear or pulling direction side of the lawnmower, is approximately 10 cm, so that this edge serves at the same time as a safety stand-off device.
It is to be understood, however, that, with pushing handles mounted so that they can be adjusted lengthwise, the grass clearing plate on the rear side is entirely dispensed with.
In practice, it has been found to be particularly advantageous if the grass clearing plate, as viewed in the direction of movement of the lawnmower, is approximately crescent-shaped and concave relative to the lawnmower housing.
Clearing the grass by means of the grass clearing plate is facilitated by a rate of revolution adjuster for the stepwise adjustment of the rate of revolution of the blade of the lawnmower. By the stepwise setting of the rate of revolution, especially with air cushion lawnmowers, an adjustment for all lawn types and conditions is achieved, such as hard, soft, thin, thick, long or short grass, and all weather conditions, such as damp or wet grass. Thus, the grass is not simply chopped up or squashed, but is cut off and can be taken by means of the grass clearing plate which is provided in accordance with the teachings of the invention. For example, the rate of revolution of the blade should be particularly low with thin grass, clover and other weeds, in order not to chop up the grass, but to cut it off.
It should be noted that the rate of revolution of the blade should be as low as possible, while still maintaining the air cushion effect, preferably about 3200 rpm, so that the grass is not chopped up excessively but rather is ejected and left lying in a bulky form whereby it can be caught and stored by the grass clearing plate. In other words, if the air cushion lawnmower blade is driven with a high rate of revolution, the grass is drawn into the air funnel more strongly than with a lower rate of revolution, so that it is then more squashed and bruised. This is in contrast to the grass receiving devices of wheeled lawnmowers, where the grass is cut off at the blade point and immediately blown into the grass receiving device.
The present construction promotes cutting instead of chopping up of the grass. This is achieved since the rotary blade is sharpened at its free end over at least one third of the half blade length, and in particular has, on both sides, a cutting edge from the end to its pivot, in the blade rotation direction.
The rotary lawnmower according to the invention can, above all, function as an air cushion lawnmower, and in particular in its preferred embodiment, has a rate of revolution adjustment and/or at least a partially continuous cutting edge on each side of the blade to be used in any weather, especially wet weather. Moreover, on account of the cutting instead of the former chopping up, the load on the drive motor is less, which not only increases its life but also, in the case of an internal combustion engine, considerably reduces its fuel consumption, so that it causes appreciably less pollution of the environment on account of the corresponding reduction in the exhaust gases.